1. Field of the Invention
The invention relates generally to polyurethane coatings possibly useful as antifouling coatings.
2. Description of the Related Art
Today's modern self-polishing systems are solvent based and are based on either tributyl tin methacrylate copolymers, tributyl silyl methacrylate copolymers or copper acrylate copolymers. A second technology is largely based on wood rosin chemistry and is supposed to replenish the surface by a kind of ablative action. Tributyl tin methacrylate copolymers are being phased out due to environmental considerations. These polymers were the workhorse for the marine industry for the last 25 years.
Tributyl silyl methacrylate copolymers have the advantage of being totally free of any heavy metals. They are however extremely expensive and this has slowed down their acceptance in the very competitive marine market.
Copper acrylate copolymers do function very well and can be produced competitively but suffer from high leaching rates of copper ions which will eventually lead to a phasing out. Ablative antifoulings are also based on the release of copper ions and might have to be phased out as well for environmental considerations.
All the above-mentioned technologies are solvent based and it will be extremely difficult to meet the ever-increasing limitations on solvent emissions. Only the silyl acrylate technology allows for formulations to be free of any heavy metal ions and to formulate totally biodegradable antifoulings.
The marine market needs longer lasting antifoulings that will allow longer dry docking intervals. This currently requires the use of multiple coats of antifouling, which leads to longer drying times and mechanically weaker films due to solvent entrapment, which are subject to mechanical damage.